Filter inductors have seen widespread use in linear and switching power supplies. Low pass filters are required in almost every power conversion application to reduce input and output ripple currents of a power supply. In linear converters where sinusoidal AC inputs are rectified to various DC levels, low-pass filters are required to prevent the undesired AC components from appearing at the output terminals of the converter. In switching power supply converters the inductor requirements are even greater. In addition to the low-pass filter requirements of the switching converter, inductors are used to store and transfer energy, and to block or reduce large current pulses during each switching cycle. All switching power supply converters switch a DC voltage at a relatively high frequency, transform the signal, then rectify the high frequency AC to a DC output. As a result of the high frequency switching and large current pulsing, Electromagnetic Interference (EMI) filters are required to block voltage spikes, switching harmonics, and associated noises generated within the switching converter. EMI filters are also required to reduce susceptibility problems due to conducted and radiated interferences from the outside world.
Typically, a low-pass or EMI filter consists of some type of series inductance and associated shunt capacitance. The series inductance must have the characteristics of a high value of inductance with a low series resistance, resulting in a relatively low power loss for the filter. A filter may also consist of multiple series and common mode inductance stages separated by shunt capacitance between each stage for maximum low-pass and EMI filtering of a DC signal. In the past, this has been achieved by winding a single coil about a magnetic core for each discrete inductance requirement. Magnetic integration can be used to combine multiple series and common mode windings on a single magnetic core resulting in inductor designs of lower cost, size, weight and even improved efficiency.